Securities (Summary of Gross Unrealized Losses and Fair Value of the Investments with Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	$ (26,872)	$ (38,606)
Less than 12 Months Fair Value	799,158	254,666
Less than 12 Months Unrealized Losses	(25,125)	(5,923)
12 Months or More Fair Value	67,664	13,378
12 Months or More Unrealized Losses	(4,619)	(377)
Total Fair Value	866,822	268,044
Total Unrealized Losses	(29,744)	(6,300)
Available-for-sale Debt Securities, Gross Unrealized Loss, instant	(29,744)	(6,300)
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	(12,538)	(16,719)
Less than 12 Months Fair Value	385,222	167,739
Less than 12 Months Unrealized Losses	(12,567)	(5,090)
12 Months or More Fair Value	64,044	12,204
12 Months or More Unrealized Losses	(4,430)	(336)
Total Fair Value	449,266	179,943
Total Unrealized Losses	(16,997)	(5,426)
Available-for-sale Debt Securities, Gross Unrealized Loss, instant	(16,997)	(5,426)
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	(13,824)	(20,893)
Less than 12 Months Fair Value	101,176	20,413
Less than 12 Months Unrealized Losses	(2,935)	(383)
12 Months or More Fair Value	807	210
12 Months or More Unrealized Losses	(47)	(5)
Total Fair Value	101,983	20,623
Total Unrealized Losses	(2,982)	(388)
Available-for-sale Debt Securities, Gross Unrealized Loss, instant	(2,982)	(388)
US Government Corporations and Agencies Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	(483)	(851)
Less than 12 Months Fair Value	290,257	56,600
Less than 12 Months Unrealized Losses	(8,942)	(435)
12 Months or More Fair Value	0	0
12 Months or More Unrealized Losses	0	0
Total Fair Value	290,257	56,600
Total Unrealized Losses	(8,942)	(435)
Available-for-sale Debt Securities, Gross Unrealized Loss, instant	(8,942)	(435)
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	0	(39)
Less than 12 Months Fair Value	20,217	9,914
Less than 12 Months Unrealized Losses	(657)	(15)
12 Months or More Fair Value	0	0
12 Months or More Unrealized Losses	0	0
Total Fair Value	20,217	9,914
Total Unrealized Losses	(657)	(15)
Available-for-sale Debt Securities, Gross Unrealized Loss, instant	(657)	(15)
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities Gross Unrealized Gain, instant	(27)	(104)
Less than 12 Months Fair Value	2,286	0
Less than 12 Months Unrealized Losses	(24)	0
12 Months or More Fair Value	2,813	964
12 Months or More Unrealized Losses	(142)	(36)
Total Fair Value	5,099	964
Total Unrealized Losses	(166)	(36)
Available-for-sale Debt Securities, Gross Unrealized Loss, instant	$ (166)	$ (36)